The present invention is directed to multicomponent pressure-sensitive adhesives based on crosslinkable olefin polymers, which enter into free radical initiated crosslinking reactions to enhance adhesive performance in admixture with compatible tackifying additives. The preferred polymers provide pendant groups having olefinic unsaturation.
Properties of unsaturated pressure sensitive adhesive compositions can be improved by use of actinic radiation, such as ultraviolet (UV) radiation; electron beam (EB) radiation; and chemical or thermal cure. Normally, the adhesive is applied to a facestock and/or a release liner and subjected to a suitable curing action to improve adhesive properties.
One means of cure is electron beam (EB) radiation. While the facestock and/or release liner can sustain electron beam dosages up to a certain level, e.g., 80 to 100 kiloGray (kGy), going beyond that level can result in degradation of components of adhesive label and tape constructions such as the face stock and/or release liner and/or adverse reactions between the adhesive and the silicon release agent of the release liner.
Increased radiation requirements, whether EB or actinic, will reduce the speed at which an adhesive coated substrate can pass under the radiating surface or increase the required number of radiating surfaces. Both are costly.
Ethylene-propylene based pressure sensitive adhesives have not found wide use in the adhesive industry. European Patent Publication 178062 assigned to Uniroyal Co. disclosed a pressure sensitive adhesive based on ethylene propylene thermoplastic elastomer comprising crystalline polypropylene sequences and amorphous ethylene-propylene sequences along the chain. Such polymers are claimed to have good balance of peel, shear and tack properties.
European Patent Publication 254002 to Takao et al disclosed a pressure sensitive adhesive with enhanced tack comprising an elastomer, tackifier and low molecular weight ethylene-propylene copolymer obtained by oxidative degradation.
U.S. Pat. No. 4,756,337 assigned to Royston Labs Inc. disclosed a tackified ethylene propylene pressure sensitive adhesive tape for sealing gas pipe lines.
The present invention is directed to pressure-sensitive adhesives based on tackified olefin polymers which utilize free radical cure to achieve a positive modification in a pressure sensitive adhesive. The pressure sensitive adhesives are formed of at least two components, one a crosslinkable olefin polymer component preferably providing pendant groups having olefinic unsaturation and another mutually compatible organic tackifying component, preferably one which minimizes the energy requirements to achieve cure or crosslinking of the olefin polymer.